Question
The chemical and physical properties of water make it an essential medium for life.
a) Outline how water acts as a coolant when sweating.
b) Describe how the kidney regulates water when the body is dehydrated.
c) Explain how water is transported from the soil to the atmosphere in flowering plants.
▶️Answer/Explanation
Explanation:
Outline how water acts as a coolant when sweating.
Water acts as a coolant during sweating due to its high specific heat capacity and high heat of vaporization. When the body becomes too hot, sweat glands release water (sweat) onto the skin. As sweat evaporates, it absorbs heat from the body, cooling it down. This process occurs because:
- Evaporation of water requires energy (heat), which is taken from the skin’s surface.
- Since water has a high heat of vaporization, it can absorb a lot of heat before it changes from liquid to gas.
- This cooling effect helps regulate body temperature and prevent overheating.
Describe how the kidney regulates water when the body is dehydrated.
When the body is dehydrated, the kidneys play a crucial role in conserving water to maintain fluid balance. The process works as follows:
- Increased Antidiuretic Hormone (ADH) secretion: The hypothalamus detects dehydration, signaling the pituitary gland to release more ADH (also called vasopressin) into the bloodstream.
- ADH effects on kidneys: ADH acts on the nephrons in the kidneys, specifically the collecting ducts, making them more permeable to water.
- Water reabsorption: As a result, more water is reabsorbed from the urine back into the bloodstream, concentrating the urine and reducing water loss.
- Conservation of water: This process helps maintain body water levels and prevents excessive fluid loss during dehydration.
Explain how water is transported from the soil to the atmosphere in flowering plants.
Water is transported from the soil to the atmosphere in a process called transpiration, which involves several steps:
- Root absorption: Water is absorbed from the soil by the plant’s roots through osmosis.
- Xylem transport: Water moves from the roots up through the xylem vessels to the leaves, using a combination of root pressure and capillary action.
- Evaporation from leaves: Once the water reaches the leaves, it evaporates from the stomata (small pores on the leaf surface) into the atmosphere. This evaporation is driven by sunlight and heat.
- Transpiration pull: As water evaporates from the stomata, it creates a vacuum that pulls more water up from the roots through the xylem, continuing the cycle.
Question
The Chinese pangolin (Manis pentadactyla) is a critically endangered species that has declined in numbers by 80% since 2000. It inhabits both forest and grassland, where it uses long, powerful claws to open ant and termite nests and ingests the insects using a long, sticky tongue.
(a) (i) State with a reason whether pangolins are autotrophic or heterotrophic.
(ii) Explain what information is needed to find the trophic level of pangolins.
(b) Pangolins are unique among mammals in having evolved scales, which are a recognition feature of reptiles. Explain which features you expect pangolins to have, which would show that they are mammals, not reptiles.
(c) The Chinese pangolin, Manis pentadactyla, has a diploid chromosome number of 40.
(i) State how many chromosomes there would be in gametes of this species.
(ii) Sex is determined in the same way in pangolins as in humans. State how many autosomes there are in somatic cells of M. pentadactyla.
Answer/Explanation
Explanation:
(a) (i) Are pangolins autotrophic or heterotrophic?
- Answer: Pangolins are heterotrophic.
- Reason: Heterotrophs are organisms that cannot make their own food and must consume other organisms for energy. Pangolins feed on ants and termites, so they are heterotrophs, unlike plants, which are autotrophic and can make their own food through photosynthesis.
(a) (ii) What information is needed to find the trophic level of pangolins?
- Answer: To determine the trophic level of pangolins, we need to know:
- What they eat: Pangolins consume insects (mainly ants and termites).
- Trophic level of their prey: The insects they eat are primary consumers (herbivores). Since pangolins eat these primary consumers, they would be secondary consumers.
- Food chain context: Understanding whether pangolins are at the second or third trophic level (depending on if they eat other secondary consumers) is essential.
(b) Explain which features show that pangolins are mammals, not reptiles.
Answer: Despite having scales, pangolins are mammals because:
- Hair: They are born with hair, a mammalian characteristic. Even though they develop scales later, all mammals have some form of hair at some point in life.
- Mammary glands: Female pangolins feed their young with milk from mammary glands, which is a defining feature of mammals.
- Live birth: Pangolins give birth to live young, unlike reptiles that mostly lay eggs.
- Endothermic (warm-blooded): Pangolins regulate their internal body temperature, a trait of mammals, while reptiles are cold-blooded.
(c) Chromosome number and sex determination in Manis pentadactyla (Chinese Pangolin)
(i) How many chromosomes in gametes?
- Answer: Gametes (sperm and egg cells) are haploid, meaning they have half the number of chromosomes in somatic cells.
- Since the diploid number of chromosomes in pangolins is 40, the haploid number in gametes is:
40 ÷ 2 = 20 chromosomes.
(ii) How many autosomes in somatic cells?
- Answer: In somatic cells, pangolins have 40 chromosomes in total. They follow the XY sex determination system (like humans), so one pair is sex chromosomes (XY for males, XX for females).
- Therefore, the number of autosomes (non-sex chromosomes) is:
40 total chromosomes – 2 sex chromosomes = 38 autosomes.
Question
The diagram shows water molecules as they might be arranged in liquid water and the interactions between them.
(a) (i) State how many water molecules are shown in the diagram.
(ii) Identify the interactions that are shown between the water molecules.
(b) (i) With reference to the diagram, explain how water in sweat evaporates.
(ii) Outline the reasons for secretion of sweat in humans.
Answer/Explanation
Explanation:
(a) (i) How many water molecules are shown in the diagram?
Answer: The number of water molecules can be counted directly in the diagram, as each “V”-shaped structure represents one water molecule.
(a) (ii) Identify the interactions that are shown between the water molecules.
Answer: The interactions are hydrogen bonds between the water molecules, formed due to the attraction between the partial positive charge on hydrogen and the partial negative charge on oxygen.
(b) (i) Explain how water in sweat evaporates.
Answer: Water molecules on the surface of sweat absorb heat, break hydrogen bonds, and transition from liquid to gas, evaporating and cooling the body.
(b) (ii) Outline the reasons for secretion of sweat in humans.
Answer: Sweat helps in:
- Cooling the body via evaporation.
- Excreting waste like urea and salts.
- Hydrating the skin to prevent dryness.
Question
a. Draw a labelled diagram to show the fluid mosaic model of the plasma membrane. [4]
b. Outline how neurons generate a resting potential. [4]
c. Hydrogen bonds can exist both within and between molecules in living organisms and have an impact on their structure and function. Explain the importance of hydrogen bonding for living organisms. [7]
▶️Answer/Explanation
Explanation:
a. Fluid mosaic model of the plasma membrane.
b. Neurons generate a resting potential through the following steps:
- Ion distribution: There is a difference in ion concentration between the inside and outside of the neuron. Higher concentrations of sodium (Na⁺) are outside the neuron, while potassium (K⁺) is higher inside the neuron.
- Sodium-potassium pump: This pump actively transports 3 Na⁺ ions out and 2 K⁺ ions in, using ATP energy. This creates a net negative charge inside the neuron relative to the outside.
- Permeability of the membrane: The membrane is more permeable to K⁺ ions than Na⁺ ions. Therefore, K⁺ ions tend to leak out of the neuron, further contributing to the negative charge inside.
- Resting potential: The result is a resting potential of around -70mV inside the neuron, with the inside being more negative compared to the outside.
- Structure of Biomolecules: In DNA, hydrogen bonds hold complementary bases (adenine-thymine, guanine-cytosine) together, ensuring stability and replication of genetic material.
- Water Properties: Hydrogen bonds give water its high specific heat, surface tension, and solvent properties, essential for temperature regulation and nutrient transport.
- Protein Folding: Hydrogen bonds stabilize the 3D structure of proteins, which is vital for their function, including enzyme activity and catalysis.
- Cell Membrane Integrity: In the plasma membrane, hydrogen bonds help maintain the fluidity and structure of the phospholipid bilayer, crucial for transport and communication.
- Biochemical Reactions: Enzymes rely on hydrogen bonding for substrate binding and catalysis in metabolic reactions.
- Cell Signaling: Hydrogen bonds between receptors and ligands facilitate communication between cells, impacting hormone signaling and immune responses.
- DNA Replication and Transcription: Hydrogen bonds allow the DNA strands to separate easily for replication and transcription, essential for genetic expression and inheritance.